I tried sucking on the vacuum hose going to the distributor, as suggested in various posts, and nothing in the distributor moved. Is this really a good way to test the vacuum advance? If not, I have to drive to Harbor Freight tomorrow for a vacuum pump to do the test. Hoping to not drive to HF as it is a 60 mile round trip. Car is a stock 1965 Skylark 300 with a four barrel.
Some vac advance cans are tight and you can’t pull enough vacuum yourself to move it. You could hook it up to a manifold vacuum source while it’s running and find out. Also, if you are not getting any resistance while trying it yourself, then the diaphragm is shot.
Be sure that at idle your not looking to have advance if your hooked up to a ported vacuum source. as posted, if your vacuum can is good then if you manually move it it will return itself to its resting position.
It should move, either by mouth (should work) or from a manifold vacuum source (as mentioned). If you are sucking air, the diaphragm is bad, as mentioned. If nothing moves and you can get a vacuum on the line ( you can feel it with your tongue) then something is frozen from dirt, rust, corrosion. Disassemble and inspect. You can take the vacuum advance canister off and do the same test. If it moves off the distributor then you need to take the distributor apart and clean and lubricate it.
Take the distributor cap off. Remove the vacuum hose from the VA canister. Move the link all the way into the canister, and at the same time cap of the vacuum nipple with your finger. The link should maintain it's position and not move. If it does, the diaphragm is leaking, and you should replace the VA.
Push the plunger in. Block the tube with your finger. Release the plunger. It should take 2 or 3 seconds to extend.
